1. Field of the Invention
The present invention relates to an image display control device and the like, which output screen display driving signals to an electronic paper display that displays a refresh screen before updating and displaying the screen.
2. Description of the Related Art
As a measure for displaying contents, recently, a contents display device for substituting paper has been socially demanded. Examples of such contents display device are a browser terminal having a display screen of A5 to A4 size with which news updated on time (e.g., latest newspaper contents automatically distributed from a server) can be viewed, and a large-scaled advertisement bulletin board having a display screen of A2 to A1 size or larger put up in train stations and the like. Such contents display devices are required to exchange contents by being radio-connected to a server and to operate in low power consumption without imposing a load on environments by receiving supply of power from a secondary battery, a solar battery, and the like.
In this case, it is desirable to structure the contents display device with a display of a large screen having a high-definition memory characteristic and a display circuit of low power consumption with a small number of components. For example, a contents display device called a book viewer Kindle, which is a product of Amazon.com.Inc., carries an A6-size electronic paper display having the resolution of SVGA (Super Video Graphics Array, 800×600 pixels) using a microcapsule-type electrophoresis display element that is a product of E Ink Corporation of US. This product has a function capable of radio-connecting to contents servers via the Internet, and books, blogs, newspapers, magazines, and the like are directly downloaded and displayed on the electronic paper display online without using a personal computer.
FIG. 15 is a schematic sectional view showing a display unit of an electronic paper display of this kind Hereinafter, explanations will be provided by referring to this drawing.
This electronic paper display uses a microcapsule-type electrophoresis display element. A display unit 80 is formed by laminating a TFT (Thin Film Transistor) glass substrate 81, an electrophoresis element film 82, and a counter substrate 83. TFTs 84 as switching elements and pixel electrodes 85 connected to the TFTs 84 are provided on the TFT glass substrate 81. In the electrophoresis element film 82, microcapsules 87 of about 40 μm are spread all over inside a polymer binder 86. A solvent 88 is impregnated inside the micro capsules 87, and an infinite number of negatively charged white pigments 89 and positively charged black pigments 90 in a nano-level size float in the solvent 88. In the counter substrate 83, a counter electrode 91 for giving a reference potential is formed.
In the display section 80, a voltage corresponding to image data is applied between the pixel electrode 85 and the counter electrode 91, so that the white pigments 89 and the black pigments 90 move up and down. For example, provided that the counter electrode 91 side is the display screen, when a positive voltage is applied to the pixel electrode 85, the negatively charged white pigments 89 move close to the pixel electrode 85. Thus, black is displayed. In the meantime, when a negative voltage is applied to the pixel electrode 85, the positively charged black pigments 90 move close to the pixel electrode 85. Thus, white is displayed. Further, the electrophoresis display element has the memory characteristic. Therefore, a negative voltage is applied when switching the pixel data of an image from white to black, while applying a positive voltage when switching the pixel data from black to white. Further, when displaying the pixel data from white to white and from black to black, “0 V” is to be applied. That is, for driving the electronic paper display, the signal voltage to be applied to the electrophoresis display element is determined by comparing a previous screen with a next screen.
Next, a general explanation of the electronic paper display using the electrophoresis display element will be provided.
With an active-matrix type display device such as a liquid crystal display device, normally, the whole image on one frame is switched by having 1/60 (=16.6) ms (milliseconds) as one frame. In the meantime, with the electronic paper display using the electrophoresis display element, the response speed of the electrophoresis display element is slow. Thus, the screen cannot be switched unless the voltage is continuously applied over a plurality of frame periods. Therefore, pulse width modulation (PWM) drive, which continuously apply a certain voltage for a plurality of frame periods, is conducted. The driving waveform in the pulse width modulation drive is determined with a lookup table based on previous screen data and update screen data. Then, a plurality of data frames are generated with the lookup table, and the pixel array of the electrophoresis display elements is addressed based on the data frames.
It becomes possible to make selections from a two-value monochrome update mode, a multi-value gradation update mode, and the like by preparing a plurality of lookup tables. Note here that the monochrome update mode is used for an electrophoresis display element having two important optical states such as black and white, and it is suited for displaying typed characters and lines, for example. An image update period under the monochrome update mode is in an order of 400 ms, since the transition time by an electrophoresis ink (pigment) is relatively long. The gradation update mode requires more time for properly writing a prescribed gradation level on the display unit. For the image update period under the gradation update mode, about 1000 ms is required in a case of four gradation levels, i.e., white, light gray, dark gray, and black, for example.
As an example of a driving method of the above-described electronic paper display, there is a driving method of a bistable electronic optical display depicted in Japanese Unexamined Patent Publication 2007-249230 (Patent Document 1). This method includes a stage of accepting drawing information of a keyboard, a touch screen, a pointer, or the like and determining at least one drawing mode waveform based on the drawing information, and a stage of addressing the pixel array of the electrophoresis display element based on the drawing information and the drawing mode waveform.
That is, in the case disclosed in Patent Document 1, a drawing mode of an electronic paper controller is determined based on the drawing information transmitted from a host such as a CPU (Central Processing Unit), and update of the drawing is conducted thereby. More specifically, the host such as the CPU transmits the pixel information such as the lookup table (data frame time, information regarding drawing, driving waveform, and the like), image data (keyboard input, drawing input, pointer input, or the like), etc., to an electronic paper controller. Then, the electronic paper display updates the screen based on the pixel information.
Further, Japanese Unexamined Patent Publication 2004-101746 (Patent Document 2) discloses a case of determining update timings of image data by using a timer for reducing the load of a CPU in an electronic paper display. Japanese Unexamined Patent Publication 2007-163987 (Patent Document 3) discloses a case of displaying a refresh screen before updating and displaying a screen in an electronic paper display.
Japanese Unexamined Patent Publication 2002-116733 (Patent Document 4: see paragraph 0095) and Japanese Unexamined Patent Publication 2002-116734 (Patent Document 5: see paragraph 0114) disclose a technique which updates a screen by applying a prescribed voltage to pixel electrodes in a period according to a difference between a gradation to be displayed next and a current gradation in an electrophoresis display device.
Japanese Unexamined Patent Publication 2008-158162 (Patent Document 6: see Abstract) discloses a technique which invalidates motion compensation between an n-th frame and an (n+1)-th frame in a case where an image of an (n−1)-th frame and an image of the n-th frame are substantially the same in an image display device.
Japanese Unexamined Patent Publication 2009-092906 (Patent Document 7: see Abstract) discloses a technique which suppresses flickers generated due to switching of the polarities in a liquid crystal display device through controlling not to invert the polarity of the liquid crystal driving voltage, when the number of counted the time (the difference between index values of two consecutive frames reaches a threshold value) exceeds a prescribed value.
Japanese Unexamined Patent Publication 2007-530984 (Patent Document 8: see Abstract) discloses a technique which suppresses power consumption of an electrophoresis display panel through updating only sub-groups of pixels that display a gray scale of a current image frame, which is different from a gray scale displayed on a previous image frame.
Incidentally, there is a market where an electronic paper display is used for a character display board which displays “hold breath”, etc., when taking an X-ray, and displays directions for the casts in TV stations, for example. In such market, there already exists a system for enabling displays on an LCD (Liquid Crystal Display). Thus, it is required to enable displays on an electronic paper display without changing the existing LCD display system.
In that case, the host such as the CPU does not transmit image data at the timing where the screen of the electronic paper display switches. The host continuously transmits the image data in the same manner as the case of transmitting the image data to the LCD, and the electronic paper controller receives the transmitted image data. At this time, as depicted in Patent Document 2, it is assumed that the electronic paper controller captures or samples the image data and updates the screen in a prescribed period. In that case, the screen of the electronic paper display becomes switched in a blinking manner because the electronic paper display displays an update screen after inserting a refresh screen configured with a black display or a white display to a previous screen. As a result, even the screens of the same display content are switched in a blinking manner in a prescribed period. Thus, in the above-described case, for example, the user may misunderstand the instruction to “hold breath” once again.
Therefore, with the electronic paper display, an algorithm for judging whether or not to rewrite the screen is required in addition to capturing and sampling the screen data in a prescribed period for the image data inputted continuously. Further, regarding whether or not to perform rewriting, it is preferable to be able to autonomously select each of the driving modes by automatically detecting whether it is screen update for a movement like a moving picture of a mouse or screen update for a sill picture, since there is a case that requires a movement like a moving picture of the mouse or the like depending on the usages.
The reason for selecting the moving-picture screen update and the still-picture screen update in the electronic paper display is as follows. In a case of the moving-picture screen update by keyboard input, drawing input, pointer input, or the like, required is a relatively short image update time. That is, it is important for the visibility to instantly update the drawing, the typing characters, and the like. Thus, it is necessary to execute the update in a shorter time than the time length of 400 ms to 1000 ms, which is the typical update speed of the electronic paper display. Therefore, the instant responsiveness (=update speed) is prior to the beautifulness and preciseness of the drawing. In the meantime, in a case of updating a text including a still picture such as a PDF file, at least 16 gradients or more is required, and gradient as well as beautifulness and preciseness of the drawing are prior to the update speed. As described, the priority items for the screen update vary for the moving-picture screen update and the still-picture update, and it is necessary to switch the driving mode based thereupon.
As described above, it is presupposed that the image is updated in the electronic paper display of the related technique by a request from the host (CPU). Thus, a special update signal is required when using an existing LCD display system. However, there is no such consideration being taken. Therefore, when the electronic paper display is to be connected to the existing LCD display system without applying a major change to the system, the screen becomes switched in a prescribed period according to the image data transmitted continuously. Thus, even when the same information is being displayed, the user may misunderstand that new information is displayed.
Therefore, it is preferable for the electronic paper display to autonomously judge whether or not to update the screen and whether to perform the moving-picture screen update or the still-picture screen update. However, there is no related technique which discloses with what algorithm the image data is captured and sampled, and the screen is rewritten in regards to the image data transmitted continuously.
It is therefore an exemplary object of the present invention to disclose an image display control device and the like, which can properly display an image on an electronic paper display even when the image data is transmitted continuously from a host of an existing LCD display system, for example.